Electronic devices and components are operating at ever increasing speeds and over increasing frequency ranges. For this reason, electronic device packages can become a source of performance degradation, often leading high-frequency system designers to dispense with a package altogether. Such “bare die” approaches frequently give inconsistent performance as the devices are subjected to environmental stresses to a greater degree than packaged devices. Commonly available high-frequency packages, often constructed from metal and ceramic laminates, address some of the concerns imparted by standard package approaches in that they bring controlled-impedance planar waveguide structures such as microstrip and coplanar waveguide (CPW) interconnects very close to the device. Device and waveguide are then connected by a short wire bond, ribbon bond, or flip-chip bump. While this provides a performance improvement, bonds and bumps still do not comprise waveguide structures, and therefore create signal mismatch at each occurrence. Solitary bonds and bumps are inductors at high frequencies, and therefore a matching network structure is typically constructed on the device, package, or printed circuit board (PCB) in order to cancel the effect of the inductance.
This solution then results in frequency range or bandwidth limitations for the device-package-PCB system. A further drawback of this approach is that the typical high-frequency package is much more expensive than its common low-frequency counterpart, which is usually fabricated from a single layer of metal and transfer or injection molded plastic.
There is clearly a need to provide a high-frequency package that has the cost structure of low-frequency packages, while providing performance suitable for high-frequency systems. Such a package would ideally take advantage of the low-cost molded plastic lead-frame package infrastructure and would have waveguide interconnects from the device all the way to the PCB. One additional constraint would be that the completed package would be compliant with generally accepted norms for standard pick-and-place and solder attach to the PCB. Package attach approaches that are exotic or non-standard will add to the overall cost of such a solution.
Previous attempts have been made to address the aforementioned issues. For example, U.S. Pat. No. 5,323,533 to Christian Val discloses a surface mount package whose wire bonds and external package leads have controlled impedance, and a coaxial structure. Unfortunately, the transition regions from internal wire bond terminal to the external leads are not controlled in their impedance, and are unshielded. Additionally, the external leads necessitate exotic lead attachment means that are not generally available in industry, impacting the cost-structure and adoptability of such an approach.
In another example, U.S. Pat. No. 5,522,132 to Carmela J. Maffei, attempts to address the shortcomings of the aforementioned approach by creating what is described as “ . . . a quasi-coaxial transmission line through the insulating substrate.” The patent teaches that their feed-through approach permits the electrical impedance to be controlled. This approach, while an improvement in some aspects, requires a non-standard package attachment method to be employed, and is not generally compatible with low-cost molded plastic lead-frame approaches, as it requires multiple isolated metallic components that are neither attached to central die-attachment surface nor to a lead frame periphery.
U.S. Pat. No. 5,622,898 to John H. Zechman discloses insulator-coated wires in circuit packaging, and describes the main advantages of such a procedure as precluding short circuiting due to movement of wires during encapsulation. The inventor also mentions the possibility of metal coatings on the insulator-coated wires to reduce inductance and electrical noise. There is no mention of impedance match, nor are the interconnect transitions considered. There is also no mention of any package configuration, including surface mount packages.
U.S. Pat. No. 6,639,305 B2 to Jerry L. Carter, et al, describes a surface mount package suitable for use at higher frequencies that does take advantage of low-cost molded plastic lead-frame approaches. The approach has the potential to be low-cost and is compliant with industry standard lead-attach means. The patent states that the construction will allow “ . . . efficient transmission of signals higher than a few GHz.” The limitation to a few GHz is due to the fact that the interconnect structure is not designed to be impedance matched, nor does it comprise a waveguide or transmission line interconnect. The described interconnect is an unshielded lead, in which “ . . . the next level assembly incorporates the necessary impedance matching . . . ” by which one skilled in the art would take to mean that elements external to the package should be used to compensate the lumped-inductance of the lead. As was previously described, this approach still results in frequency range or bandwidth limitations for the device-package-PCB system. In addition, the approach ignores the impact of cross talk from the unshielded lead.
U.S. Pat. No. 6,770,822 B2, filed by some of the same applicants for the current Invention, describes a surface mount package with integral shielding and controlled impedance from the circuit device to the PCB, with good high frequency performance attributes. The use of coaxial vias, while excellent from an electrical performance and possible package hermeticity standpoint, necessitates exotic lead attachment means that are not generally available in industry, impacting the cost-structure and adoptability for low-cost applications of such an approach. Additionally, the coaxial package utilizes a construction approach that is not generally available in the package industry, adding further to the cost-structure limitations.
Thus, it is desirable to provide a high frequency package and method of making the same and it is to this end that the disclosure is directed.